Holt Algebra 1

6-1 Solving Systems by Graphing6-1 Solving Systems by Graphing

Holt Algebra 1

Warm Up

Lesson Presentation

Lesson Quiz

Holt Algebra 1

6-1 Solving Systems by Graphing

Bell Quiz 6-1Evaluate each expression for x = 1 and y =–3.

1. x – 4y

Write each expression in slope-intercept form.

2. y – x = 1

2 pts

3 pts

5 pts

possible

Holt Algebra 1

6-1 Solving Systems by Graphing

Identify solutions of linear equations in two

variables.

Solve systems of linear equations in two variables by graphing.

Objectives

Holt Algebra 1

6-1 Solving Systems by Graphing

systems of linear equations

solution of a system of linear equations

Vocabulary

Holt Algebra 1

6-1 Solving Systems by Graphing

A system of linear equations is a set of two or more linear equations containing two or more variables. A solution of a system of linear equations with two variables is an ordered pair that satisfies each equation in the system. So, if an ordered pair is a solution, it will make both equations true.

Holt Algebra 1

6-1 Solving Systems by Graphing

Tell whether the ordered pair is a solution of the given system.

Example 1A: Identifying Systems of Solutions

(5, 2);

3x – y = 13

Holt Algebra 1

6-1 Solving Systems by Graphing

If an ordered pair does not satisfy the first equation in the system, there is no reason to check the other equations.

Helpful Hint

Holt Algebra 1

6-1 Solving Systems by Graphing

Example 1B: Identifying Systems of Solutions

Tell whether the ordered pair is a solution of the given system.

(–2, 2);x + 3y = 4

–x + y = 2

Holt Algebra 1

6-1 Solving Systems by Graphing

Check It Out! Example 1a

Tell whether the ordered pair is a solution of the given system.

(1, 3); 2x + y = 5

–2x + y = 1

Holt Algebra 1

6-1 Solving Systems by Graphing

Check It Out! Example 1b

Tell whether the ordered pair is a solution of the given system.

(2, –1); x – 2y = 43x + y = 6

Holt Algebra 1

6-1 Solving Systems by Graphing

All solutions of a linear equation are on its graph. To find a solution of a system of linear equations, you need a point that each line has in common. In other words, you need their point of intersection.

y = 2x – 1

y = –x + 5

The point (2, 3) is where the two lines intersect and is a solution of both equations, so (2, 3) is the solution of the systems.

Holt Algebra 1

6-1 Solving Systems by Graphing

Sometimes it is difficult to tell exactly where the lines cross when you solve by graphing. It is good to confirm your answer by substituting it into both equations.

Helpful Hint

Holt Algebra 1

6-1 Solving Systems by Graphing

Solve the system by graphing. Check your answer.

Example 2A: Solving a System Equations by Graphing

y = x

y = –2x – 3

Holt Algebra 1

6-1 Solving Systems by Graphing

Solve the system by graphing. Check your answer.

Example 2B: Solving a System Equations by Graphing

2x + y = 4

Holt Algebra 1

6-1 Solving Systems by Graphing

Solve the system by graphing. Check your answer.Check It Out! Example 2a

y = –2x – 1

y = x + 5

Holt Algebra 1

6-1 Solving Systems by Graphing

Example 3: Problem-Solving Application

Wren and Jenni are reading the same book. Wren is on page 14 and reads 2 pages every night. Jenni is on page 6 and reads 3 pages every night. After how many nights will they have read the same number of pages? How many pages will that be?

Holt Algebra 1

6-1 Solving Systems by Graphing

1 Understand the Problem

The answer will be the number of nights it takes for the number of pages read to be the same for both girls. List the important information:

Wren on page 14 Reads 2 pages a night

Jenni on page 6 Reads 3 pages a night

Example 3 Continued

Holt Algebra 1

6-1 Solving Systems by Graphing

2 Make a Plan

Write a system of equations, one equation to represent the number of pages read by each girl. Let x be the number of nights and y be the total pages read.

Totalpages is

number read

everynight plus

already read.

Wren y = 2 • x + 14

Jenni y = 3 • x + 6

Example 3 Continued

Holt Algebra 1

6-1 Solving Systems by Graphing

Solve3

Example 3 Continued

•

(8, 30)

Nights

Graph y = 2x + 14 and y = 3x + 6. The lines appear to intersect at (8, 30). So, the number of pages read will be the same at 8 nights with a total of 30 pages.

Holt Algebra 1

6-1 Solving Systems by Graphing

Look Back4

Check (8, 30) using both equations.

Number of days for Wren to read 30 pages.

Number of days for Jenni to read 30 pages.

Example 3 Continued

Holt Algebra 1

6-1 Solving Systems by Graphing

HOMEWORK�Section 6-1 (page 386) 2, 5, 9-13, 28, 29, 33-35 (5, 12, 13: Graph to solve and (5, 12, 13: Graph to solve and (5, 12, 13: Graph to solve and (5, 12, 13: Graph to solve and enter answer in online)enter answer in online)enter answer in online)enter answer in online)

Holt Algebra 1

6-1 Solving Systems by Graphing

HOMEWORK